8th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA), 13 – 16 November, 2017, New Zealand

INQUA Focus Group Earthquake Geology and Seismic Hazards

The role of surface-rupturing faults in the Waiautoa microblock, Clarence valley, New Zealand, during the Mw 7.8

Langridge, Robert (1), Ries, William (1), Rowland, Julie (2), Villamor, Pilar (1), Kearse, Jesse (3), Little, Timothy (3), Nissen, Edwin (4), Madugo, Chris (5), Litchfield, Nicola (1), Gasston, Caleb (2), Hall, Brendon (2), Canva, Albane (2), Hatem, Alex (6), Zinke, Robert (6).

(1) Active Landscapes Dept., GNS Science, PO Box 30-368, Lower Hutt, New Zealand. Email: [email protected]; [email protected] (2) Dept. of Earth Sciences, University of Auckland, New Zealand (3) Dept. of Earth Sciences, Victoria University of Wellington, Wellington, New Zealand (4) School of Earth and Ocean Sciences, Victoria University, British Columbia, Canada (5) Pacific Gas and Electric, Kensington, California USA. (6) Dept. of Earth Sciences, University of Southern California, Los Angeles, California, USA

Abstract: The Mw 7.8 Kaikōura Earthquake has presented an opportunity to study the scale of earthquake deformation from regional-scale, to individual block and micro-block tectonics. The 2.5 km2 ‘Waiautoa microblock’ refers to the high-angle fault intersection area between the co-seismic ruptures of the Jordan, Kekerengu, Papatea, and Waiautoa faults in the Clarence valley. Detailed field observations and post-earthquake LiDAR mapping indicate that these faults intersect in a complex, triangular fashion. The Jordan Thrust (dextral-normal in 2016) overlaps the dextral-reverse Kekerengu Fault near George Stream. In this same area, ruptures of the reverse-sinistral Papatea Fault almost intersect the Jordan Thrust. To close the triangle, the reverse- sinistral Waiautoa Fault is inferred to link the Papatea with the Kekerengu Fault. Assessment of piercing line markers indicates that co-seismic surface slip increases to the NE of George Stream, and is largely conserved along the length of the Waiautoa microblock as the Jordan, Kekerengu and Waiautoa faults share and exchange 7-9 m of surface slip. Summed co-seismic surface slip within the Waiautoa microblock is sub-equal to co-seismic surface slip on the Kekerengu Fault northeast of the microblock, suggesting that this zone of complexity promoted the continuation of surface rupture.

Key words: Waiautoa Fault, Papatea Fault, , transpression.

INTRODUCTION Langridge et al., 2016a) (Fig. 1). The vast majority of seismic energy and surface slip was released during the second half The 14 November 2016 (local time) Mw 7.8 Kaikōura of the earthquake sequence when rupture of the northern earthquake, New Zealand is one of the largest, high-slip faults within the MFS, initiated and propagated slip to the onshore earthquakes to have occurred in recent times northeast (e.g. Kaiser et al., 2017). (Hamling et al., 2017; Kaiser et al., 2017; Stirling et al., 2017). Surface rupture occurred on at least 14 named faults between Waiau in north Canterbury and offshore of Cape Campbell, Marlborough over c. 160 km (Fig. 1). The pattern of surface faulting is highly complex both at the full scale of the rupture and at smaller scales where individual faults or fault segments interact with adjoining faults. This paper documents an important complexity near the centre of the Kaikōura earthquake rupture zone where 5 distinct faults – the Jordan, Kekerengu, Papatea, Fidget and Waiautoa faults - join and overlap one another in three dimensions.

The Kaikōura earthquake occurred in the central part of the Australia-Pacific plate boundary through New Zealand in the northeastern South Island. This region is characterized by plate convergence rates of c. 37-40 mm/yr and a progression from compression in the southwest, to transpression and strike-slip motion in the northeast, across a transitional plate boundary setting where the leading edge of the Pacific plate subducts Figure 1: Map of the northern surface fault ruptures (red lines) in beneath the New Zealand margin (e.g. Wallace et al., the 2016 Mw 7.8 Kaikōura Earthquake. Blue box indicates Fig. 2 2012). Fault rupture during the Kaikōura earthquake began highlighting the Papatea Fault (PF) and Waiautoa Fault (WF). See in the North Canterbury Domain and propagated into the text for other abbreviations. (MFS) (Litchfield et al., 2014;

PROGRAMME 220 8TH INTERNATIONAL PATA DAYS 2017 8th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA), 13 – 16 November, 2017, New Zealand 8th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA), 13 – 16 November, 2017, New Zealand

INQUA Focus Group Earthquake Geology and Seismic Hazards INQUA Focus Group Earthquake Geology and Seismic Hazards

This paper describes the ‘Waiautoa microblock’ where five the hangingwall. The main reverse-sinistral trace is of the major northern faults join and overlap one another progressively concealed in George Stream (Fig. 3). and where both proximity of individual fault ruptures and The role of surface-rupturing faults in the Waiautoa microblock, Clarence valley, the partitioning of slip from one to another can be measured and documented. Understanding how faults and New Zealand, during the Mw 7.8 2016 Kaikōura Earthquake fault zones within the upper crust interact at the km-scale, with respect to the shape and size of fault stepovers and Langridge, Robert (1), Ries, William (1), Rowland, Julie (2), Villamor, Pilar (1), Kearse, Jesse (3), Little, Timothy (3), Nissen, Edwin (4), Madugo, bends is of great relevance for considering the seismic Chris (5), Litchfield, Nicola (1), Gasston, Caleb (2), Hall, Brendon (2), Canva, Albane (2), Hatem, Alex (6), Zinke, Robert (6). hazard posed by integrated fault networks (Wesnousky, 2008; Barka and Kadinsky-Cade, 2002). (1) Active Landscapes Dept., GNS Science, PO Box 30-368, Lower Hutt, New Zealand. Email: [email protected]; [email protected] (2) Dept. of Earth Sciences, University of Auckland, New Zealand (3) Dept. of Earth Sciences, Victoria University of Wellington, Wellington, New Zealand METHODOLOGY (4) School of Earth and Ocean Sciences, Victoria University, British Columbia, Canada (5) Pacific Gas and Electric, Kensington, California USA. Following the Kaikōura earthquake, we collected field (6) Dept. of Earth Sciences, University of Southern California, Los Angeles, California, USA observations where fault surface rupture was recognized and accessible, and undertook helicopter reconnaissance Abstract: The Mw 7.8 Kaikōura Earthquake has presented an opportunity to study the scale of earthquake deformation from of sites in remote areas where landing was difficult or regional-scale, to individual block and micro-block tectonics. The 2.5 km2 ‘Waiautoa microblock’ refers to the high-angle fault impractical. We employed a variety of techniques to intersection area between the co-seismic ruptures of the Jordan, Kekerengu, Papatea, and Waiautoa faults in the Clarence valley. measure surface slip including tape measure, sighting of Detailed field observations and post-earthquake LiDAR mapping indicate that these faults intersect in a complex, triangular scarp heights, real-time kinematic (RTK-GPS), total station, fashion. The Jordan Thrust (dextral-normal in 2016) overlaps the dextral-reverse Kekerengu Fault near George Stream. In this and UAV (drone) surveys. Offsets were recorded on same area, ruptures of the reverse-sinistral Papatea Fault almost intersect the Jordan Thrust. To close the triangle, the reverse- cultural features including fencelines, roads, and planted sinistral Waiautoa Fault is inferred to link the Papatea with the Kekerengu Fault. Assessment of piercing line markers indicates treelines, and geomorphic features such as stream that co-seismic surface slip increases to the NE of George Stream, and is largely conserved along the length of the Waiautoa channels, risers and scree deposits. Due to the possibility microblock as the Jordan, Kekerengu and Waiautoa faults share and exchange 7-9 m of surface slip. Summed co-seismic surface of offsets being destroyed by bad weather and/or farm slip within the Waiautoa microblock is sub-equal to co-seismic surface slip on the Kekerengu Fault northeast of the microblock, reparations and the slow availability of some airborne suggesting that this zone of complexity promoted the continuation of surface rupture. datasets, the faults were mapped and surveyed as quickly as was practical on the ground soon after the earthquake. Key words: Waiautoa Fault, Papatea Fault, 2016 Kaikoura earthquake, transpression. In early 2017 we received aerial orththomosaics and in mid-2017 post-earthquake LiDAR coverage of most of the

earthquake rupture zone. In some cases, such as along the Figure 2: 2016 co-seismic surface rupture of the Papatea Fault INTRODUCTION Langridge et al., 2016a) (Fig. 1). The vast majority of seismic coast and up the Clarence valley, pre-earthquake LiDAR (yellow) and ruptures of the Jordan (purple), Kekerengu (red) and energy and surface slip was released during the second half surveys existed (Langridge et al., 2016b). In these cases, we Waiautoa (brick) faults in the vicinity of the Waiautoa microblock The 14 November 2016 (local time) Mw 7.8 Kaikōura of the earthquake sequence when rupture of the northern developed Differential LiDAR (D-LiDAR) models of the (WM). George (GS), Miller (MS) and Mclean (McS) streams and earthquake, New Zealand is one of the largest, high-slip faults within the MFS, initiated and propagated slip to the ground surface change (Clark et al., 2017; Nissen et al., this Shag Bend (SB) are labelled. Black line marks Fig. 4 slip-section. onshore earthquakes to have occurred in recent times northeast (e.g. Kaiser et al., 2017). volume). Field and GIS data were collated to produce (Hamling et al., 2017; Kaiser et al., 2017; Stirling et al., surface rupture maps, slip vectors and slip distributions for Jordan Thrust - The Jordan Thrust is an important, 2017). Surface rupture occurred on at least 14 named individual faults (Jordan, Kekerengu, Papatea, Fidget and northeast-striking, high-slip rate plate boundary fault that faults between Waiau in north Canterbury and offshore Waiautoa) within 10 km of the Waiautoa microblock area. links the Kekerengu with the to the southwest of Cape Campbell, Marlborough over c. 160 km (Fig. 1). (Van Dissen and Yeats, 1991). Following the earthquake, The pattern of surface faulting is highly complex both at MAJOR FAULT RUPTURES ASSOCIATED WITH THE helicopter reconnaissance and limited ground the full scale of the rupture and at smaller scales where WAIAUTOA MICROBLOCK AREA observations indicated that only the northern half of this individual faults or fault segments interact with adjoining fault (as mapped) had surface rupture. Farther inland, faults. This paper documents an important complexity Papatea Fault - The Papatea Fault, which extends from parts of the Upper Kowhai Fault (UKF) and Manakau Fault near the centre of the Kaikōura earthquake rupture zone offshore in Waipapa Bay to George Stream (Fig. 2), was (MF) within the Seaward Kaikōura Range also displayed where 5 distinct faults – the Jordan, Kekerengu, Papatea, recognised as an important NNW-striking bedrock, and surface rupture. The northern half of the Jordan Thrust Fidget and Waiautoa faults - join and overlap one another possibly active, fault prior to the Kaikōura earthquake typically displayed dextral-normal (uphill-facing) surface in three dimensions. (Barrell, 2015; Rattenbury et al., 2006). Papatea fault rupture with 3-4 m dextral slip near Miller Stream and up ruptures have a variable strike along the mapped length of to 6-8 m at George Stream. Northeast of this point, the The Kaikōura earthquake occurred in the central part of the fault. They are commonly reverse-sinistral in sense Jordan Thrust overlapped with rupture on the Kekerengu the Australia-Pacific plate boundary through New Zealand with a maximum (near-field) net slip of 7.4 ± 0.6 m. D- Fault. While dextral-normal motion was observed the long- in the northeastern South Island. This region is LiDAR profiles are consistent with InSAR results that term motion for this fault is of transpression, therefore, we characterized by plate convergence rates of c. 37-40 suggest the Papatea Block (i.e. the block bounded by the entertain the possibility of a blind component of reverse mm/yr and a progression from compression in the Papatea, Jordan and Hope faults) moved vertically by 8-10 motion on the Jordan fault. southwest, to transpression and strike-slip motion in the m (and by several m to the south) (Hamling et al., 2017). northeast, across a transitional plate boundary setting Offsets on the Papatea Fault are locally sinistral-reverse Kekerengu Fault - The northeast-striking Kekerengu Fault where the leading edge of the Pacific plate subducts Figure 1: Map of the northern surface fault ruptures (red lines) in with up to 6 m of net slip at the coast across two distinct represents the longest onland rupture (c. 28 km) and largest recorder of slip (up to 11.8 m dextral) during the Kaikōura beneath the New Zealand margin (e.g. Wallace et al., the 2016 Mw 7.8 Kaikōura Earthquake. Blue box indicates Fig. 2 fault strands (Clark et al., 2017). Near the northern end of 2012). Fault rupture during the Kaikōura earthquake began highlighting the Papatea Fault (PF) and Waiautoa Fault (WF). See the fault, an impressive N-striking reverse-sinistral rupture earthquake sequence (Hamling et al., 2017; Stirling et al., in the North Canterbury Domain and propagated into the text for other abbreviations. scarp bends to the NW into a splaying, distributed zone of 2017; Kearse et al., this volume). The southern half of the Marlborough Fault System (MFS) (Litchfield et al., 2014; sinistral-normal faulting and monoclinal ruptures within fault occurs from George Stream north along the Clarence River valley. Northeast of the river, the fault traverses

8TH INTERNATIONAL PATA DAYS 2017 221 PROGRAMME 8th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA), 13 – 16 November, 2017, New Zealand

INQUA Focus Group Earthquake Geology and Seismic Hazards

farmland out to the Marlborough coast. While the highest the northwest end of rupture on the Papatea Fault and the offsets in 2016 were documented in the north, the southern Jordan Thrust at George Stream. Similarly, despite a lack of half of the fault consistently produced surface ruptures with continuous rupture or exposure, we infer that the 9-11 m of dextral slip in the floor of the Clarence River and Waiautoa Fault forms a link between the Kekerengu and across the Shag Bend area. South of Shag Bend there is an Papatea faults and forms the eastern boundary of the apparent drop in the magnitude of slip toward Waiautoa Waiautoa microblock. The translation of slip off the Station and McLean Stream, where there is c. 6 m of dextral Papatea Fault near its northern end and increased slip on slip. South of McLean Stream, surface rupture associated the Kekerengu Fault north of Waiautoa Station both with the Kekerengu Fault is dextral-normal in sense and equate with a slip and kinematic transfer from these faults coincides with pre-existing geomorphology within the onto the Waiautoa Fault. rangefront (Fig. 3). Where it could be measured the slip between McLean Stream and George Stream decreased from c. 6 to 2 m and effectively to zero where the fault bends to the southwest to become the Fidget Fault.

Waiautoa Fault - The north-striking Waiautoa Fault is a short (3.4 km) reverse-sinistral slip fault that ruptured during the Kaikōura earthquake with slip up to c. 1 m. The presence of the Waiautoa Fault is coincident with the course of the Clarence River and Tertiary bedrock structure. In the north, the fault splays from the Kekerengu Fault and is characterized by reverse-slip rolls, thrusts and folds that generally follow pre-existing topography such as risers and alluvial fans. The fault proceeds south toward the Waiautoa homestead, where a reverse-slip rupture with 20-40 cm up-to-the-west motion is Figure 3: View to the northeast at George Stream, which is mapped across McLean stream in LiDAR images. The impounded by dextral-normal slip on the Jordan Thrust, and cuts a swath through the native forest. The overlapping rupture of the Waiautoa Fault is projected to the south according to the Kekerengu Fault is upslope to the left of this photo. presence of surface ruptures and ridge-crest extension,

toward the Clarence River bridge. Abutments of the bridge DISCUSSION appear to be offset sinistrally by c. 1 m.

Observations THE WAIAUTOA MICROBLOCK – INTERPRETATION Mapping using a variety of tools indicates that the

Waiautoa microblock forms a kinematic complexity at the Careful mapping and surveying has allowed for the southern end of the Jordan-Kekerengu-Needles rupture connection and correlation of the five mapped faults set within the 2016 Kaikōura earthquake sequence. This whose junction area form a 2.5 km2 triangular area - the 2.5 km2 fault junction area has accommodated the Waiautoa microblock. The Fidget Fault bends from an ENE transpressional strain release of five distinct faults or to NE strike to merge with the Kekerengu Fault at the SW fault segments in a single earthquake, dominated by corner of the microblock. Minor to zero surface rupture slip dextral slip, but including reverse and sinistral motion. on the Fidget Fault evolves abruptly into full surface These five faults yield slip vectors consistent with the rupture of the Kekerengu Fault with slip increasing from c. northeast to eastward kinematic motion across faults 6 to 10-12 m dextral in the northeast beyond the Waiautoa (relative to the coast and plate boundary). Rupture microblock. Multi-metre dextral slip on the Jordan Thrust through this complexity (microblock) heralded the 2nd reaches a peak at the southwestern end of the microblock half of the complex Kaikōura earthquake sequence with at George Stream. To the north, rupture of the Jordan the highest slips and strongest ground motions; thus the Thrust continues immediately east of, and overlapping complexity did not act to inhibit rupture, rather it was with, the Kekerengu Fault, converging from an across- central to a burst of fault ruptures, the timings of which strike width of 350 m between surface ruptures to an can only be deduced from seismology (Kaiser et al., 2017; observed minimum of <100 m (Fig. 3). In this overlap zone, Duputel and Rivera, 2017). Simplified slip distributions there is a trade-off or sharing of fault slip between the (Fig. 4) indicate that 7-11 m of slip consistently passes Jordan and Kekerengu faults. For example, at the southern into, or out of, the Waiautoa microblock area, thus either: part of this overlap at George Knob a single long fenceline 1) slip is: essentially conserved at a first order across the crosses both faults with 3.2 ± 0.4 m dextral slip on the microblock, or 2) rupture energy (and therefore slip) former and 3.4 ± 0.4 m on the latter (Fig. 4). Toward the grew out of the basin to reach a peak on the northern end northern convergence of the Jordan-Kekerengu fault of the Kekerengu Fault. overlap, the Jordan Thrust appears more and more to be a

thrust fault that partners the Kekerengu Fault. Implications

We can learn a lot about rupture process from 3rd order The Papatea Fault almost certainly extends to the complexities involved in such complex earthquake southwest corner of the Waiautoa microblock, though ruptures. For example: there is a lack of visible surface slip over c. 1.4 km between

PROGRAMME 222 8TH INTERNATIONAL PATA DAYS 2017 8th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA), 13 – 16 November, 2017, New Zealand 8th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology (PATA), 13 – 16 November, 2017, New Zealand

INQUA Focus Group Earthquake Geology and Seismic Hazards INQUA Focus Group Earthquake Geology and Seismic Hazards

farmland out to the Marlborough coast. While the highest the northwest end of rupture on the Papatea Fault and the 1) faults can join with hard or soft linkages in 3-D both in a REFERENCES offsets in 2016 were documented in the north, the southern Jordan Thrust at George Stream. Similarly, despite a lack of mappable sense and in an individual earthquake rupture. half of the fault consistently produced surface ruptures with continuous rupture or exposure, we infer that the The result of this is that it is important to map faults at the Barka, A., Kadinsky-Cade, K. (1988). Strike-slip fault geometry in 9-11 m of dextral slip in the floor of the Clarence River and Waiautoa Fault forms a link between the Kekerengu and scale to which it is relevant, i.e. if a fault is being mapped Turkey and its influence on earthquake activity. Tectonophysics across the Shag Bend area. South of Shag Bend there is an Papatea faults and forms the eastern boundary of the for a critical facility or structure, such as a city, dam or 7: 663-684. Barrell, D.J.A. (2015). General distribution and characteristics of apparent drop in the magnitude of slip toward Waiautoa Waiautoa microblock. The translation of slip off the nuclear facility, then the detail and the complexity that active faults and folds in the Kaikoura District, North Station and McLean Stream, where there is c. 6 m of dextral Papatea Fault near its northern end and increased slip on need to be considered are greater (e.g. Petersen et al., Canterbury. GNS Science Consultancy Report 2014/210. 59 p. slip. South of McLean Stream, surface rupture associated the Kekerengu Fault north of Waiautoa Station both 2010). This paper highlights that because the Kaikōura Barth, N.C., Toy, V.G., Langridge, R.M., and Norris, R.J. (2012). with the Kekerengu Fault is dextral-normal in sense and equate with a slip and kinematic transfer from these faults ruptures have often been mapped at a scale of 1:1000, Scale dependence of oblique plate boundary partitioning: new coincides with pre-existing geomorphology within the onto the Waiautoa Fault. then far more complexity and a greater array of structures insights from LiDAR, central , New Zealand: rangefront (Fig. 3). Where it could be measured the slip can be observed. This is also true for faults that can be Lithosphere 4: 435-448. between McLean Stream and George Stream decreased mapped using airborne LiDAR and other digital datasets Clark, K.J. and 14 others (2017). Highly variable coastal from c. 6 to 2 m and effectively to zero where the fault bends (e.g. Barth et al., 2012). deformation in the 2016 Mw 7.8 Kaikoura earthquake reflects to the southwest to become the Fidget Fault. rupture complexity along a transpressional plate boundary. Earth and Plan. Science Lett.: doi: 10.1016/j.epsl.2017.06.048. Duputel, Z., Rivera, L. (2017). Long-period analysis of the 2016 Waiautoa Fault - The north-striking Waiautoa Fault is a short Kaikoura earthquake. Physics of the Earth and Planetary (3.4 km) reverse-sinistral slip fault that ruptured during the Interiors 265: 62–66. Kaikōura earthquake with slip up to c. 1 m. The presence of Freund, R. (1971). The Hope Fault: A strike-slip fault in New the Waiautoa Fault is coincident with the course of the Zealand. New Zealand Geological Survey Bulletin 86: 49 p. Clarence River and Tertiary bedrock structure. In the north, Hamling, I.J.; and 28 others. 2017 Complex multifault rupture the fault splays from the Kekerengu Fault and is characterized during the 2016 Mw 7.8 Kaikoura earthquake, New Zealand. by reverse-slip rolls, thrusts and folds that generally follow Science, 356 (6334): doi: 10.1126/science.aam7194. Kaiser, A.E.; and 25 others (2017). The 2016 Kaikoura, New pre-existing topography such as risers and alluvial fans. The Zealand, earthquake: preliminary seismological report. fault proceeds south toward the Waiautoa homestead, where Seismol. Res. Letters, 88(3): 1-13; doi: 10.1785/0220170018. a reverse-slip rupture with 20-40 cm up-to-the-west motion is Figure 3: View to the northeast at George Stream, which is Kearse, J. and 11 others (2017). Surface rupture and slip mapped across McLean stream in LiDAR images. The impounded by dextral-normal slip on the Jordan Thrust, and cuts a distribution of the Kekerengu Fault during the Mw 7.8 2016 swath through the native forest. The overlapping rupture of the Waiautoa Fault is projected to the south according to the Kaikoura Earthquake. (this volume) Kekerengu Fault is upslope to the left of this photo. presence of surface ruptures and ridge-crest extension, Langridge RM, and 14 others (2016a). The New Zealand Active Figure 4: Simplified slip distribution across the Waiautoa toward the Clarence River bridge. Abutments of the bridge Faults Database. New Zealand Journal of Geology and DISCUSSION microblock summing motion from the Jordan, Kekerengu and appear to be offset sinistrally by c. 1 m. Geophysics 59 (1): doi:10.1080/00288306.2015.1112818. Waiautoa faults. Slip profile projected normal to Kekerengu Fault Langridge, R.M.; Ries, W.F.; Barth, N.; Howarth, J.D.; Quigley, M.;

Observations and includes dextral and reverse motion (see black line on Fig. 2). Farrier, T. (2016b). Assembling lidar swaths along the South THE WAIAUTOA MICROBLOCK – INTERPRETATION Mapping using a variety of tools indicates that the Island plate boundary, New Zealand: the South Island 'b4'

Waiautoa microblock forms a kinematic complexity at the 2) faults can communicate in 3-D to effectively ‘share’ slip project. 4 p. IN: McCalpin, J.P.; Gruetzner, C. (eds.) Proceedings Careful mapping and surveying has allowed for the of the 7th International Workshop on Paleoseismology, Active southern end of the Jordan-Kekerengu-Needles rupture across a complexity. In the context of the Waiautoa Basin, connection and correlation of the five mapped faults Tectonics and Archaeoseismology ("PATA Days"), Crestone, set within the 2016 Kaikōura earthquake sequence. This the Jordan and Kekerengu faults overlap one another to whose junction area form a 2.5 km2 triangular area - the Colorado, USA. Crestone, Colo. 2.5 km2 fault junction area has accommodated the share slip, while the Kekerengu and Papatea faults Waiautoa microblock. The Fidget Fault bends from an ENE accommodate the complex transition from dextral-reverse Litchfield, N.J. and 19 others 2014. A model of active faulting in transpressional strain release of five distinct faults or New Zealand. N.Z. J. Geol. Geophys. 57: 32-56. to NE strike to merge with the Kekerengu Fault at the SW to reverse-sinistral motion via the reverse-sinistral slip fault segments in a single earthquake, dominated by Nissen, E., Raghu Malireddi, S., Clark, K., Hamling, I., Langridge, R., corner of the microblock. Minor to zero surface rupture slip dextral slip, but including reverse and sinistral motion. Waiautoa Fault. Ries, W., Tagliasacchi, A. (2017). Three-dimensional coastal on the Fidget Fault evolves abruptly into full surface These five faults yield slip vectors consistent with the 3) small transpressive complexities such as the Waiautoa deformation in the Mw 7.8 Kaikōura earthquake from rupture of the Kekerengu Fault with slip increasing from c. northeast to eastward kinematic motion across faults microblock may not be rupture inhibitors, but rather differential airborne lidar. (this volume). 6 to 10-12 m dextral in the northeast beyond the Waiautoa Petersen, M.D., Dawson, T.E., Chen, R., Cao, T., Wills, C.J., (relative to the coast and plate boundary). Rupture rupture promoters, or ‘kickers’. Rupture of faults microblock. Multi-metre dextral slip on the Jordan Thrust Schwartz, D.P., Frankel, A.D. (2017). Fault displacement hazard through this complexity (microblock) heralded the 2nd surrounding the Waiautoa microblock were involved in reaches a peak at the southwestern end of the microblock for strike-slip faults. Bull. Seismol. Soc. America 101: 805-825. half of the complex Kaikōura earthquake sequence with kicking off the 2nd half of the Kaikōura earthquake at George Stream. To the north, rupture of the Jordan sequence. When such features are mapped for seismic Rattenbury, M.S., Townsend, D.B., Johnston, M.R. (compilers) the highest slips and strongest ground motions; thus the (2006). Geology of the Kaikoura area. Inst. of Geological & Thrust continues immediately east of, and overlapping source or hazard purposes they should not necessarily be complexity did not act to inhibit rupture, rather it was Nuclear Sciences 1:250,000 geological map 13. 1 sheet + 70 p. with, the Kekerengu Fault, converging from an across- considered as a structural complexity that will halt central to a burst of fault ruptures, the timings of which Stirling, M.W. and 56 others (2017). The Mw 7.8 Kaikoura strike width of 350 m between surface ruptures to an can only be deduced from seismology (Kaiser et al., 2017; through-going fault rupture. earthquake: surface fault rupture and seismic hazard context. observed minimum of <100 m (Fig. 3). In this overlap zone, Duputel and Rivera, 2017). Simplified slip distributions 4) finally, along with the long histories of bedrock and Bull. N. Z. Society for Earthquake Engineering, 50(2): 73-84. there is a trade-off or sharing of fault slip between the Stirling, M.W. and 19 others, 2012. National Seismic Hazard Model (Fig. 4) indicate that 7-11 m of slip consistently passes geomorphic fault offsets on individual faults of the MFS Jordan and Kekerengu faults. For example, at the southern for New Zealand: 2010 Update: Bull. Seismological Soc. into, or out of, the Waiautoa microblock area, thus either: (Freund, 1971), the Waiautoa microblock must be part of this overlap at George Knob a single long fenceline America, v. 102, p. 1514-1542, doi: 10.1785/0120110170. 1) slip is: essentially conserved at a first order across the considered a long-lived geomorphic and kinematic feature crosses both faults with 3.2 ± 0.4 m dextral slip on the as it is responsible for developing secondary topography Van Dissen, R.; Yeats, R. S. (1991). Hope fault, Jordan thrust, and uplift microblock, or 2) rupture energy (and therefore slip) of the Seaward Kaikoura Range, New Zealand. Geology 19: 393-396. former and 3.4 ± 0.4 m on the latter (Fig. 4). Toward the and controls both the short term passage of the Clarence grew out of the basin to reach a peak on the northern end Wallace, L.M. and 8 others (2012). The kinematics of a transition northern convergence of the Jordan-Kekerengu fault of the Kekerengu Fault. River, and its long-term history, sitting at the southern end from subduction to strike-slip: An example from the central overlap, the Jordan Thrust appears more and more to be a of a 12 km deflection of this important river. New Zealand plate boundary. Journal of Geophysical Research, thrust fault that partners the Kekerengu Fault. Implications 117, B02405, doi:10.1029/2004JB003241. Acknowledgements: We wish to thank those agencies that Wesnousky, S.G. (2008). Displacement and geometrical We can learn a lot about rupture process from 3rd order The Papatea Fault almost certainly extends to the funded post-earthquake mapping efforts including GeoNet, NSF, characteristics of earthquake surface ruptures: Issues and complexities involved in such complex earthquake southwest corner of the Waiautoa microblock, though MBIE and GEER. This paper was reviewed by Phaedra Upton. implications for seismic-hazard analysis and the process of ruptures. For example: there is a lack of visible surface slip over c. 1.4 km between earthquake rupture. Bull. Seismol. Soc. America 98: 1609-16.

8TH INTERNATIONAL PATA DAYS 2017 223 PROGRAMME